Document locking

Hi, I just had a brief look at the the CMIS specification (1 minute or so), and I did not immediately find anything related to locking (i.e. to avoid two people updating the same document around the same time, the last person overwriting the work of the first person without either of them knowing it.). Is this handled by the checkin/checkout functionality or is there something else?

Ps: I found it frustrating that there is no central CMIS resource. You have to go and discuss at one of the supporting vendors discussion forums if you have questions / feedback on the spec.